Aspect Ratio Calculator
Three related calculations in one place. Given a width and a height, it reduces them to an exact whole-number ratio — and it does mean exact: 1920 × 1080 is 16:9, but 1366 × 768 is 683:384 and is not quite 16:9, a distinction most calculators quietly round away and the reason a 1366-wide screenshot ends up with thin black bars on a 16:9 display. Given a ratio and one dimension, it works out the other and flags when the answer does not land on a whole pixel. Given an original size and a bounding box, it works out the largest size that fits without distorting the picture. A reference table of the common ratios and where each is used sits underneath.
How it works
An aspect ratio is the width of an image compared with its height, reduced to whole numbers. The reduction here is exact: 1920 × 1080 is 16:9, but 1366 × 768 is 683:384 and is not quite 16:9 — a distinction most calculators quietly round away, and the reason a 1366-wide screenshot has thin black bars on a 16:9 display.
Enter a width and height to see the ratio they make.
Details
This is exactly 16:9 — HD and 4K video, most monitors and phone screens in landscape.
Common aspect ratios
What each one is normally used for.
| Ratio | Decimal | Where you see it |
|---|---|---|
| 16:9 | 1.778 | HD and 4K video, most monitors and phone screens in landscape |
| 4:3 | 1.333 | Classic monitors, iPad, older broadcast television |
| 3:2 | 1.5 | 35mm film and most DSLR sensors |
| 1:1 | 1 | Square — Instagram posts and profile pictures |
| 21:9 | 2.333 | Ultrawide monitors and anamorphic cinema |
| 9:16 | 0.563 | Vertical video — Reels, Shorts, TikTok, Stories |
| 5:4 | 1.25 | Large-format photography and some print sizes |
| 2:3 | 0.667 | Portrait photo prints, 4×6 inch |
| 1.85:1 | 1.85 | Standard cinema widescreen |
| 2.39:1 | 2.39 | Anamorphic scope, the widest common cinema format |
| 1.618:1 | 1.618 | The golden ratio |
Frequently asked questions
What is an aspect ratio?
The width of an image compared with its height, reduced to whole numbers. 1920 × 1080 reduces to 16:9, which is why that ratio describes almost all modern video.
Why does 1366 × 768 not come out as 16:9?
Because it genuinely is not — it reduces to 683:384, which is about 0.06% wider than 16:9. Calculators that report 16:9 are rounding, and that rounding is why 16:9 content shows thin bars on such a screen.
How do I find the height for a given width?
Use the second tab: choose the ratio, say which dimension you know, and enter it. The other is calculated, with a note if it does not fall on a whole pixel.
What does "resize to fit" do?
It finds the largest size that fits inside a bounding box while keeping the ratio — the sum behind "make this fit within 1200 × 800 without stretching it".
Which aspect ratio should I use for social media?
1:1 for a square feed post, 9:16 for stories and short-form vertical video, and 16:9 for landscape video. The reference table lists the rest.
Do I need to upload an image?
No — this is pure arithmetic on the numbers you type. No image is involved at all.
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